excited-state intramolecular proton-transfer reaction … · 2015. 10. 12. · s1 supplementary...
TRANSCRIPT
S1
Supplementary Information
for
Excited-State Intramolecular Proton-Transfer Reaction
Demonstrating Anti-Kasha Behavior
Huan-Wei Tseng,a,‡ Jiun-Yi Shen,
a,‡ Ting-Yi Kuo,
a Ting-Syun Tu,
a Yi-An Chen,
a
Alexander P. Demchenkob,
* and Pi-Tai Choua,
*
a Department of Chemistry, National Taiwan University, Taipei, 10617 Taiwan
b Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kiev 01030,
Ukraine
‡ These authors contributed equally to this work.
Electronic Supplementary Material (ESI) for Chemical Science.This journal is © The Royal Society of Chemistry 2015
S2
Contents
Page
Experimental Details S-3
Fig. S1 The X-ray structure of the doubly hydrogen-bonded 3-HTC-DICN dimers
in the crystalline state.
S-6
Fig. S2 The 1H NMR spectroscopy of 3-HTC-DiCN in THF-d8. S-6
Fig. S3 Absorption and emission spectra for 3-HTCA in different solvents. S-7
Fig. S4 Absorption and emission spectra for 3-HTC-DiCN in different solvents. S-7
Fig. S5 Relative emission spectra for 3-HTCA in CH2Cl2 with different excitation
wavelengths.
S-8
Fig. S6 Absorption, emission (excited at 320 nm and 400 nm) and excitation
spectra (monitored at indicated wavelengths) for 3-HTC-DiCN-OMe in
CH2Cl2
S-8
Fig. S7 Absorption, emission (excited at 350 nm) and excitation spectra
(monitored at indicated wavelengths) for 3-HTC in CH2Cl2.
S-9
Fig. S8 Nanosecond time-resolved emission decays for 3-HTC-DiCN recorded in
CH2Cl2.
S-9
Fig. S9 Fluorescence up-conversion time-resolved kinetic traces for 3-HTCA in
CH2Cl2 (excited at 400 nm).
S-10
Fig. S10 Fluorescence up-conversion time-resolved kinetic traces for 3-HTCA in
CH2Cl2 (excited at 350 nm).
S-11
Fig. S11 Fluorescence up-conversion time-resolved kinetic traces for 3-HTC-
DiCN in CH2Cl2 (excited at 350 nm).
S-12
Fig. S12 Fluorescence up-conversion time-resolved kinetic traces for 3-HTC-
DiCN in CH2Cl2 (excited at 425 nm).
S-13
Table S1 Single crystal data and structure refinements for 3-HTC-DiCN S-14
Table S2 Bond lengths and angles in the crystal structure of 3-HTC-DiCN S-15
Table S3 Emission rise and decay lifetimes in the fs-ps time range for 3-HTCA in
CH2Cl2 with different excitation wavelengths (λex) and monitored at
various emission wavelengths (λem)
S-16
Table S4 Emission rise and decay lifetimes in the fs-ps time range for 3-HTC-
DiCN in CH2Cl2 with different excitation wavelengths (λex) and
monitored at various emission wavelengths (λem)
S-17
Calculations and Discussions on the Proton Transfer Efficiencies from the
Higher Energy States
S-18
S3
Experimental Details
Synthesis and Characterizations
All reactions were carried out in oven- or flame-dried glassware under a positive pressure of
N2. All reagents were purchased commercially and used without further purification. TLC was
performed on Merck 5715 silica gel 60 F254 pre-coated plates. Flash column chromatography
was carried out using silica gel from Merck (230-400 mesh). 1H-NMR (7.24 ppm for residual
CHCl3 in the CDCl3 solvent as internal standard) and 13
C-NMR (77.0 ppm for CDCl3 as internal
standard) spectra were recorded on a Varian Unity-400 MHz instrument. Chemical shifts (δ) are
quoted in parts per million (ppm) and coupling constants (J) are reported in Hertz (Hz). MS data
was obtained using a Shimadzu LCMS-IT-TOF Mass Spectrometer. Single-crystal X-ray
diffraction data were acquired on a Bruker SMART CCD diffractometer using λ (Mo-Kα)
radiation (λ = 0.71073 Å). The data collection was executed using the SMART program. Cell
refinement and data reduction were carried out with the SAINT program. The structure was
determined using the SHELXTL/PC program and refined using full-matrix least squares. All
non-hydrogen atoms were refined anisotropically, whereas hydrogen atoms were placed at
calculated positions and included in the final stage of refinements with fixed parameters.
3-HTC. A mixture of thiophene-2-carbaldehyde (1.12 g, 10 mmol), 2-hydroxyacetophenone
(1.36 g, 10 mmol), and NaOH (1.20 g, 30 mmol) in MeOH (60 mL) was heated under reflux for
5 h. The reaction mixture was cooled to room temperature. NaOH(aq) (1.0 N, 30 mL) and then
hydrogen peroxide (35%, 4.5 mL) were added. After stirring overnight, the mixture was poured
into ice-water and extracted with dichloromethane. The organic layer was dried over MgSO4,
filtered and evaporated. The crude product was purified by recrystallization from CH2Cl2 and
hexane to yield 3-HTC as a yellow solid (1.46 g, 60%). 1H NMR (400 MHz, CDCl3): δ 8.22 (dd,
J = 8.0, 1.2 Hz, 1H), 8.00 (dd, J = 4.0, 1.2 Hz, 1H), 7.70-7.65 (m, 1H), 7.60 (dd, J = 5.2, 1.2 Hz,
1H), 7.56 (d, J = 8.4 Hz, 1H), 7.41-7.37 (m, 1H), 7.24-7.21 (m, 1H), 6.93 (s, 1H). 13
C NMR (100
MHz, CDCl3): δ 172.5, 155.0, 142.6, 136.3, 133.5, 132.9, 129.8, 129.7, 128.1, 125.4, 124.5,
121.0, 118.1. FAB MS (m/z): 245 (M+H)+.
3-HTCA. A mixture of 5-(1,3-dioxolan-2-yl)thiophene-2-carbaldehyde (1.84 g, 10 mmol), 2-
hydroxyacetophenone (1.36 g, 10 mmol), and NaOH (1.20 g, 30 mmol) in MeOH (60 mL) was
heated under reflux for 5 h. The reaction mixture was cooled to room temperature. NaOH(aq) (1.0
N, 30 mL) and then hydrogen peroxide (35%, 4.5 mL) were added to the mixture for stirring
overnight. The mixture was evaporated and adjusted to pH 5 using 1.0 N HCl(aq). After extraction
with dichloromethane, the organic layer was dried over MgSO4, filtered and evaporated. The
crude product was purified by recrystallization from CH2Cl2 and hexane to yield 3-HTCA as a
yellow solid (1.11 g, 40%). 1H NMR (400 MHz, CDCl3): δ 9.99 (s, 1H), 8.23 (d, J = 7.6 Hz, 1H),
8.05 (d, J = 4.0 Hz, 1H), 7.83 (d, J = 4.0 Hz, 1H), 7.73 (t, J = 7.6 Hz, 1H), 7.57 (d, J = 8.4 Hz,
1H), 7.43 (t, J = 8.4 Hz, 1H). 13
C NMR (100 MHz, CDCl3): δ 183.0, 172.7, 155.2, 145.4, 141.5,
140.5, 138.0, 136.1, 134.3, 129.3, 125.5, 124.9, 120.8, 118.2. FAB MS (m/z): 273 (M+H)+.
S4
3-HTC-DiCN. A mixture of 3-HTCA (0.70 g, 2.5 mmol), malononitirile (0.83 g, 12.5 mmol),
and a catalytic amount of piperidine in THF (30 mL) and MeOH (30mL) was stirred for 3 days.
The solid was filtered and washed with CH2Cl2 and MeOH to yield 3-HTC-DiCN as an orange
solid (0.30 g, 38%). 1H NMR (400 MHz, THF-d8): δ 10.2 (s, 1H), 8.35 (s, 1H), 8.17 (dd, J = 8.0,
2.0 Hz, 1H), 8.07 (d, J = 4.0 Hz, 1H), 7.96 (d, J = 4.8 Hz, 1H), 7.77-7.73 (m, 1H), 7.65 (d, J =
8.0 Hz, 1H), 7.44-7.40 (d, J = 8.0 Hz, 1H). 13
C NMR (100 MHz, THF-d8): δ 173.1, 156.0, 152.0,
144.0,141.3, 140.7, 139.0, 138.7, 134.7, 129.2, 126.1, 125.4, 123.0, 118.9, 114.9, 114.3, 79.0.
FAB MS (m/z): 321 (M+H)+. The orange-red crystals of 3-HTC-DiCN were grown in a THF
solution. The crystal structure is shown in Fig. S1 and the crystal data, bond lengths, and angles
are listed in Table S1 and S2.
3-HTCA-OMe. A mixture of thiophene-2-carbaldehyde (0.56 g, 5.0 mmol), 2-
hydroxyacetophenone (0.68 g, 5.0 mmol), and NaOH (0.60 g, 15 mmol) in MeOH (30 mL) was
heated under reflux for 5 h. The reaction mixture was cooled to room temperature. NaOH(aq) (1.0
N, 15 mL) and then hydrogen peroxide (35%, 2.3 mL) were added. After stirring overnight, the
mixture was poured into ice-water and extracted with dichloromethane. The organic layer was
dried over MgSO4, filtered and evaporated to form 1 and which was used in the next reaction
without further purification. A mixture of 1 and DBU (1 mL) in dimethyl carbonate (40 mL) was
heated under reflux for 2 days. The solvent was evaporated under reduced pressure. The residue
was added into 1N HCl (50 mL) and extracted with ethyl acetate. The organic layer was dried
over MgSO4, filtered and evaporated. The crude product was purified by silica gel column
chromatography with hexane/EtOAc mixture as eluent to afford 3-HTCA-OMe as a light-yellow
solid (0.78 g, 55%). 1H NMR (400 MHz, CDCl3): δ 10.03 (s, 1H), 8.25 (dd, J = 8.0, 1.6 Hz, 1H),
8.00 (d, J = 4.0, 1H), 7.83 (d, J = 4.4, 1H), 7.73-7.69 (m, 1H), 7.54 (d, J = 8.4 Hz, 1H), 7.44-7.40
(m, 1H), 4.15 (s, 3H). 13
C NMR (100 MHz, CDCl3): δ 183.49, 174.02, 154.81, 149.52, 146.51,
140.55, 140.05, 135.27, 133.96, 129.30, 125.88, 125.03, 124.25, 117.85, 59.93. FAB MS (m/z):
287 (M+H)+. Note that 3-HTCA-OMe is not stable and a trace amount of impurity always exists
S5
and is likely due to decomposition. The impurity makes it infeasible to perform reliable
spectroscopy studies.
3-HTC-DiCN-OMe. A mixture of 3-HTCA-OMe (0.50 g, 2.0 mmol), malononitirile (0.70 g, 10
mmol), and a catalytic amount of piperidine in THF (20 mL) and MeOH (20 mL) was heated
under reflux overnight. The solvent was evaporated under reduced pressure and the residue was
extracted with CH2Cl2. The organic layer was dried over MgSO4, filtered and evaporated. The
crude product was purified by column chromatography on silica gel with a CH2Cl2/EtOAc
mixture as eluent to afford 3-HTC-DiCN-OMe as a yellow solid (0.20 g, 30%). 1H NMR (400
MHz, CDCl3): δ 8.23 (dd, J = 8.0, 1.6 Hz, 1H), 8.00 (d, J = 4.0, 1H), 7.88 (d, J = 4.4, 1H), 7.84
(s, 1H), 7.73-7.68 (m, 1H), 7.54 (d, J = 8.4 Hz, 1H), 7.43-7.39 (m, 1H), 4.18 (s, 3H). 13
C NMR
(100 MHz, CDCl3): δ 154.79, 150.16, 140.87, 138.51, 136.81, 134.17, 129.63, 125.94, 125.20,
124.28, 117.89, 113.61, 112.94, 79.83, 60.14. FAB MS (m/z): 335 (M+H)+.
S6
Fig. S1 The X-ray structure of the doubly hydrogen-bonded 3-HTC-DiCN dimers in the
crystalline state. (The distances of the intermolecular H-bonds (O-H…O=C) are both 1.861 Å
while the intramolecular distances between the O2 atom and the H atom bounded to the O3 atom
are both estimated to be 2.464 Å.)
Fig. S2 The 1H NMR spectroscopy of 3-HTC-DiCN in THF-d8.
S7
300 400 500 600 700 8000.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0Emission in
Benzene
DCM
MeCN
Norm
aliz
ed E
mis
sio
n Inte
nsity
Norm
aliz
ed A
bsorb
ance
Wavelength (nm)
Absorption in
Benzene
DCM
MeCN
Fig. S3 Steady-state absorption and emission spectra (with 350 nm excitation) for 3-HTCA in
benzene, dichloromethane (DCM) and acetonitrile (MeCN). The low-intensity N* band appears
in the emission spectrum on a very low level.
300 400 500 600 7000.0
0.2
0.4
0.6
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0Emission in
Benzene
DCM
MeCN
Norm
aliz
ed E
mis
sio
n Inte
nsity
Norm
aliz
ed A
bsorb
ance
Wavelength (nm)
Absorption in
Benzene
DCM
MeCN
Fig. S4 Steady-state absorption and emission spectra (with 440 nm excitation) for 3-HTC-DiCN
in benzene, dichloromethane (DCM) and acetonitrile (MeCN). The presence of N* band in
emission is clearly seen.
S8
Fig. S5 Relative emission spectra for 3-HTCA in CH2Cl2 with different excitation wavelengths.
The emission intensities of the spectra are set to be the same at the peak of the normal form
emission. Insets: photos of emission hue with a shorter- or a longer-wavelength excitation.
Fig. S6 Absorption, emission (excited at 320 nm and 400 nm) and excitation spectra (monitored
at indicated wavelengths) for 3-HTC-DiCN-OMe in CH2Cl2. All the excitation spectra are
nearly identical to the absorption spectrum. The normalized emission spectra with 320 nm or 400
nm excitations are on top of each other. No extra emission bands (from higher energy states) can
be observed with 320 nm excitation (note: the band peaked at 350 nm is due to Raman
scattering). These results conclude no anti-Kasha behavior.
S9
Fig. S7 Absorption, emission (excited at 350 nm) and excitation spectra (monitored at indicated
wavelengths) for 3-HTC in CH2Cl2. The results show only minor deviation from Kasha’s rule.
Fig. S8 Nanosecond time-resolved emission decays for 3-HTC-DiCN recorded in CH2Cl2. The
excitation wavelength is 400 nm. The emission kinetic traces of the N* form (blue) and the T*
form (red) are recorded at indicated wavelengths. IRF (black) is the instrument responds function.
As in the case of 3-HTC the strong difference in long component of decays (For N* band it is
almost unresolved from IRF) indicates the non-equilibrium character of ESIPT reaction.
S10
Fig. S9 Fluorescence up-conversion time-resolved kinetic traces for 3-HTCA in CH2Cl2. (a)
Upon 400 nm excitation, the dynamics of relaxation of the normal emission acquired at different
wavelengths. (b) Excited-state tautomer (T*) emission kinetics is recorded at indicated
wavelength with a 400 nm excitation. The presence of system response limited component at
short wavelength edge of T* emission is due to ESIPT prior to solvent relaxtion.29,30
S11
Fig. S10 Fluorescence up-conversion time-resolved kinetic traces for 3-HTCA in CH2Cl2.
Excited-state tautomer (T*) emission kinetics is recorded at indicated wavelength with a 350 nm
excitation.
S12
Fig. S11 Fluorescence up-conversion time-resolved kinetic traces for 3-HTC-DiCN in CH2Cl2.
(a) A comparison of emission decays and rises at indicated excitation and emission wavelengths.
(b) Upon 350 nm excitation, the dynamics of relaxation of the normal emission acquired at
several different wavelengths. (c) Emission kinetics recorded at indicated wavelengths for the T*
emission with a 350 nm excitation.
S13
Fig. S12 Fluorescence up-conversion time-resolved kinetic traces for 3-HTC-DiCN in CH2Cl2.
(a) Upon 425 nm excitation, the dynamics of relaxation of the normal emission acquired at
different wavelengths. (b) Emission kinetics recorded at indicated wavelengths for the T*
emission with a 425 nm excitation.
S14
Table S1 Single crystal data and structure refinements for 3-HTC-DiCN
Identification code ic15823
Empirical formula C17 H8 N2 O3 S
Formula weight 320.31
Temperature 200(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group P2(1)/c
Unit cell dimensions a = 15.8828(18) Å
b = 6.8328(8) Å
c = 13.9502(16) Å
α = 90°
β =107.844(2)°
γ = 90°
Volume 1441.1(3) Å3
Z 4
Density (calculated) 1.476 Mg/m3
Absorption coefficient 0.241 mm-1
F(000) 656
Crystal size 0.32 x 0.30 x 0.02 mm3
Theta range for data collection 1.35 to 25.00°
Index ranges -18 ≤ h ≤ 18, -8 ≤ k ≤ 8, -16 ≤ l ≤ 16
Reflections collected 8334
Independent reflections 2537 [R(int) = 0.1061]
Completeness to theta = 25.00° 99.7 %
Absorption correction Semi-empirical from equivalents
Max. and min. transmission 0.9952 and 0.9268
Refinement method Full-matrix least-squares on F2
Data / restraints / parameters 2537 / 0 / 209
Goodness-of-fit on F2 1.090
Final R indices [I>2sigma(I)] R1 = 0.0669, wR2 = 0.1620
R indices (all data) R1 = 0.1021, wR2 = 0.2021
Largest diff. peak and hole 0.397 and -0.493 e.Å-3
S15
Table S2 Bond lengths and angles in the crystal structure of 3-HTC-DiCN
Bond Lengths (Å)
S(1)-C(10) 1.724(4) C(5)-C(6) 1.412(5)
S(1)-C(13) 1.736(4) C(6)-C(7) 1.444(5)
O(1)-C(9) 1.360(5) C(7)-C(8) 1.432(6)
O(1)-C(1) 1.369(5) C(8)-C(9) 1.363(5)
O(2)-C(7) 1.253(4) C(9)-C(10) 1.451(6)
O(3)-C(8) 1.352(4) C(10)-C(11) 1.383(5)
N(1)-C(16) 1.132(6) C(11)-C(12) 1.377(6)
N(2)-C(17) 1.140(6) C(12)-C(13) 1.380(6)
C(1)-C(2) 1.382(5) C(13)-C(14) 1.423(6)
C(1)-C(6) 1.397(5) C(14)-C(15) 1.349(6)
C(2)-C(3) 1.380(6) C(15)-C(16) 1.430(7)
C(3)-C(4) 1.390(6) C(15)-C(17) 1.446(6)
C(4)-C(5) 1.372(6)
Bond Angles (°)
C(10)-S(1)-C(13) 90.86(19) C(9)-O(1)-C(1) 119.6(3)
O(1)-C(1)-C(2) 115.9(4) O(1)-C(1)-C(6) 121.4(3)
C(2)-C(1)-C(6) 122.7(4) C(3)-C(2)-C(1) 117.8(4)
C(2)-C(3)-C(4) 121.4(4) C(5)-C(4)-C(3) 120.2(4)
C(4)-C(5)-C(6) 120.2(4) C(1)-C(6)-C(5) 117.6(4)
C(1)-C(6)-C(7) 119.9(4) C(5)-C(6)-C(7) 122.5(4)
O(2)-C(7)-C(8) 120.9(4) O(2)-C(7)-C(6) 123.4(4)
C(8)-C(7)-C(6) 115.6(3) O(3)-C(8)-C(9) 118.0(4)
O(3)-C(8)-C(7) 120.6(3) C(12)-C(13)-C(14) 124.2(4)
C(9)-C(8)-C(7) 121.3(4) C(12)-C(13)-S(1) 110.9(3)
O(1)-C(9)-C(8) 122.1(4) C(14)-C(13)-S(1) 124.9(3)
O(1)-C(9)-C(10) 111.1(3) C(15)-C(14)-C(13) 131.0(4)
C(8)-C(9)-C(10) 126.7(4) C(14)-C(15)-C(16) 119.6(4)
C(11)-C(10)-C(9) 125.3(4) C(14)-C(15)-C(17) 124.3(4)
C(11)-C(10)-S(1) 111.8(3) C(16)-C(15)-C(17) 116.1(4)
C(9)-C(10)-S(1) 122.9(3) N(1)-C(16)-C(15) 179.9(7)
C(12)-C(11)-C(10) 112.6(4) N(2)-C(17)-C(15) 177.5(5)
C(11)-C(12)-C(13) 113.8(4)
S16
Table S3 Emission rise and decay lifetimes in the fs-ps time range for 3-HTCA in CH2Cl2 with
different excitation wavelengths (λex) and monitored at various emission wavelengths (λem)
compound λex (nm) λem (nm) τobs by uPL (ps) pre-exponential factor
3-HTCA 350 430 3.8±0.3 0.41
25.2±3.2 0.59
460 4.6±0.7 0.29
25.8±3.9 0.71
490 2.8±0.2 -0.1
4.3±0.5 0.2
25.5±2.8 0.7
580 5.8±0.7 −0.45 a
25.4±3.0 −0.55 a
600 6.1±0.6 −0.46 a
26.2±2.6 −0.54 a
620 5.7±0.7 −0.39 a
25.8±3.4 −0.61 a
650 6.4±0.8 −0.36 a
26.2±3.1 −0.64 a
400 460 25.4±3.6 1.00
490 2.4±0.1 -0.15
25.2±3.4 0.83
580 26.3±2.6 −1.00 a
600 25.7±2.1 −1.00 a
620 26.6±3.5 −1.00 a
650 26.2±3.1 −1.00 a
a Rise kinetics.
S17
Table S4 Emission rise and decay lifetimes in the fs-ps time range for 3-HTC-DiCN in CH2Cl2
with different excitation wavelengths (λex) and monitored at various emission wavelengths (λem)
compound λex (nm) λem (nm) τobs by uPL (ps) pre-exponential factor
3-HTC-DiCN 350 470 1.3±0.2 0.58
5.6±0.8 0.42
500 1.5±0.2 0.42
5.8±0.6 0.58
530 1.3±0.2 -0.4
1.5±0.2 0.28
6.1±0.7 0.32
620 1.8±0.1 0.89
5.9±0.4 −0.11 a
650 1.7±0.2 0.64
6.1±0.9 −0.36 a
425 500 6.2±0.8 1.0
530 1.8±0.2 -0.37
6.4±0.8 0.63
620 3.8±0.4 0.90
6.1±0.6 −0.10 a
650 3.9±0.5 0.68
5.7±0.8 −0.32 a
700 4.3±0.5 0.50
5.7±0.7 −0.50 a
750 4.0±0.4 0.36
5.8±0.6 −0.64 a
770 6.0±0.8 −1.00 a
a Rise kinetics.
S18
Calculations and Discussions on the Proton Transfer Efficiencies from the Higher Energy
States
The equations needed are:
𝐼𝑁(𝛽)
𝐼𝑁(𝛼)=
𝛽
𝛼(1 − 𝑦) (𝑒𝑞. 1)
𝐼𝑇(𝛽)
𝐼𝑇(𝛼)=
𝐼𝑁(𝛽)
𝐼𝑁(𝛼)+
𝛽𝑦
𝛼𝑥 (𝑒𝑞. 3)
3-HTC-DiCN - Data taken from the absorption and excitation spectra (Fig. 4 & 5):
Wavelength
(nm)
Relative
Absorbance
Relative Emission Intensity in the
Excitation Spectrum Monitored at
Normal Form (500 nm) Tautomer Form (625 nm)
300 0.20 0.14 1.12
350 0.21 0.19 0.67
450 0.98 0.99 0.62
Using the data obtained at 350 and 450 nm:
For 350 nm, β = 0.21
450 nm, α = 0.98
𝛽
𝛼=
0.21
0.98= 0.214
For 350 nm, IN(β) = 0.19 and IT(β) = 0.67
450 nm, IN(α) = 0.99 and IT(α) = 0.62
𝐼𝑁(𝛽)
𝐼𝑁(𝛼)=
0.19
0.99= 0.192 and
𝐼𝑇(𝛽)
𝐼𝑇(𝛼)=
0.67
0.62= 1.08
Plug the values into eq. 1
0.192 = 0.214(1 − 𝑦) 𝑦 = 0.103 = 10.3%
Then by using eq. 2
1.08 = 0.192 + 0.214 ×0.103
𝑥 𝑥 = 0.025 = 2.5%
S19
Using the data obtained at 300 and 450 nm:
For 300 nm, β = 0.20
450 nm, α = 0.98
𝛽
𝛼=
0.20
0.98= 0.204
For 300 nm, IN(β) = 0.14 and IT(β) = 1.12
450 nm, IN(α) = 0.99 and IT(α) = 0.62
𝐼𝑁(𝛽)
𝐼𝑁(𝛼)=
0.14
0.99= 0.141 and
𝐼𝑇(𝛽)
𝐼𝑇(𝛼)=
1.12
0.62= 1.81
Plug the values into eq. 1
0.141 = 0.204(1 − 𝑦) 𝑦 = 0.309 = 30.9%
Then by using eq. 2
1.81 = 0.141 + 0.204 ×0.309
𝑥 𝑥 = 0.038 = 3.8%
Now, Fig. 9 can be updated by adding the new information obtained for 3-NTC-DiCN:
S20
The tautomer emission quantum yield (Φem) can be written as
Φ𝑒𝑚 = 𝑦𝜔 + (1 − 𝑦)𝑥𝜔
From Table 1, when 3-HTC-DiCN is excited at 300 nm, the tautomer emission quantum yield
(Φem) is 0.060.
0.060 = 30.9% × 𝜔 + (1 − 30.9%) × 3.8% × 𝜔
𝜔 = 0.18
The emission quantum efficiency is low, which also explains why the excited-state tautomer
lifetime is as long as 2.1 ns, but Φem is only 0.060.
Check point:
When 3-HTC-DiCN is excited at 350 nm, the tautomer emission quantum yield can be estimated
using the equation and the ω value obtained above:
Φ𝑒𝑚 = 𝑦𝜔 + (1 − 𝑦)𝑥𝜔
Φ𝑒𝑚 = 10.3% × 0.18 + (1 − 10.3%) × 2.5% × 0.18
= 0.023
From Table 1, when 3-HTC-DiCN is excited at 350 nm, the tautomer emission quantum yield
(Φem) is 0.030 which is not far off from the estimated value.
Furthermore, the observed decay lifetime of the normal form emission of 3-HTC-DiCN is about
6 ps, which corresponds to a kobs of 1.67 x 1011
s-1
. Then the ESIPT rate from the S1N state can be
calculated:
1.67 × 1011 𝑠−1 × 3.15%
= 5.26 × 109 𝑠−1
= 190 𝑝𝑠
This is a much slower rate when compared with regular ESIPT (~1 ps). This result also indicates
that proton-coupled charge transfer and solvent-induced barrier have channeled into the reaction
coordinate (See Fig. 8).
S21
When it brings to the resonance form, ESIPT is ultrafast. Also, given a fast solvent relaxation
time constant of 1 ps in CH2Cl2,
5.26 × 109𝑠−1 = 𝐴𝑒−∆𝐸 𝑅𝑇⁄
5.26 × 109𝑠−1 = 1 × 1012𝑠−1 × 𝑒−∆𝐸 𝑅𝑇⁄
𝑒−∆𝐸 𝑅𝑇⁄ = 0.00526
−∆𝐸 𝑅𝑇⁄ = 𝑙𝑛 0.00526
∆𝐸 = 5.25 × 1.986 𝑐𝑎𝑙/𝑚𝑜𝑙 ∙ 𝐾 × 300𝐾
∆𝐸 = 3.13 𝑘𝑐𝑎𝑙/𝑚𝑜𝑙, which is a very reasonable value.
A further question is why the nonradiative decay rate (1.67 x 1011
s-1
) is so fast in 3-HTC-DiCN?
The answer is likely to be the rotational motions along the single bonds in the molecule.
3-HTCA - Data taken from the absorption and excitation spectra (Fig. 3 & S5):
Wavelength
(nm)
Relative
Absorbance
Relative Emission Intensity in the
Excitation Spectrum Monitored at
Normal Form (450 nm) Tautomer Form (600 nm)
300 0.21 0.11 0.28
350 0.58 0.43 0.63
400 0.71 0.83 0.70
Using the data obtained at 350 and 400 nm:
For 350 nm, β = 0.58
400 nm, α = 0.71
S22
𝛽
𝛼=
0.58
0.71= 0.817
For 350 nm, IN(β) = 0.43 and IT(β) = 0.63
400 nm, IN(α) = 0.83 and IT(α) = 0.70
𝐼𝑁(𝛽)
𝐼𝑁(𝛼)=
0.43
0.83= 0.518 and
𝐼𝑇(𝛽)
𝐼𝑇(𝛼)=
0.63
0.70= 0.900
Plug the values into eq. 1
0.518 = 0.817(1 − 𝑦) 𝑦 = 0.366 = 36.6%
Then by using eq. 2
0.900 = 0.518 + 0.817 ×0.366
𝑥 𝑥 = 0.783 = 78.3%
Using the data obtained at 300 and 400 nm:
For 300 nm, β = 0.21
400 nm, α = 0.71
𝛽
𝛼=
0.21
0.71= 0.296
For 300 nm, IN(β) = 0.11 and IT(β) = 0.28
400 nm, IN(α) = 0.83 and IT(α) = 0.70
𝐼𝑁(𝛽)
𝐼𝑁(𝛼)=
0.11
0.83= 0.133 and
𝐼𝑇(𝛽)
𝐼𝑇(𝛼)=
1.28
0.70= 0.400
Plug the values into eq. 1
0.133 = 0.296(1 − 𝑦) 𝑦 = 0.551 = 55.1%
Then by using eq. 2
0.400 = 0.133 + 0.296 ×0.551
𝑥 𝑥 = 0.611 = 61.1%
S23
Now, the picture for 3-HTCA is
The tautomer emission quantum yield (Φem) can be written as
Φ𝑒𝑚 = 𝑦𝜔 + (1 − 𝑦)𝑥𝜔
From Table 1, when 3-HTCA is excited at 300 nm, the tautomer emission quantum yield (Φem)
is 0.32.
0.32 = 55.1% × 𝜔 + (1 − 55.1%) × 61.1% × 𝜔
𝜔 = 0.39
This emission quantum efficiency of 3-HTCA is higher than that of 3-HTC-DiCN (ω = 0.18)
and the observed excited-state tautomer lifetime for 3-HTCA (6.1 ns) is also longer than 3-
HTC-DiCN (2.4 ns).
S24
Check point:
When 3-HTCA is excited at 350 nm, the tautomer emission quantum yield can be estimated
using the equation and the ω value obtained above:
Φ𝑒𝑚 = 𝑦𝜔 + (1 − 𝑦)𝑥𝜔
Φ𝑒𝑚 = 36.6% × 0.39 + (1 − 36.6%) × 78.3% × 0.39
= 0.34
From Table 1, when 3-HTCA is excited at 350 nm, the tautomer emission quantum yield (Φem)
is 0.31 which is not far off from the estimated value.